The present invention relates generally to medical devices for forming holes in heart chamber interior walls in percutaneous myocardial revascularization (PMR) procedures. More specifically, the present invention relates to intravascular PMR devices having generally annular tips.
A number of techniques are available for treating cardiovascular disease such as cardiovascular by-pass surgery, coronary angioplasty, laser angioplasty and atherectomy. These techniques are generally applied to by-pass or open lesions in coronary vessels to restore and increase blood flow to the heart muscle. In some patients, the number of lesions are so great, or the location so remote in the patient vasculature that restoring blood flow to the heart muscle is difficult. Percutaneous myocardial revascularization (PMR) has been developed as an alternative to these techniques which are directed at by-passing or removing lesions. Heart muscle may be classified as healthy, hibernating and xe2x80x9cdeadxe2x80x9d. Dead tissue is not dead but is scarred, not contracting, and no longer capable of contracting even if it were supplied adequately with blood. Hibernating tissue is not contracting muscle tissue but is capable of contracting, should it be adequately re-supplied with blood. PMR is performed by boring channels directly into the myocardium of the heart.
PMR was inspired in part by observations that reptilian hearts muscle is supplied primarily by blood perfusing directly from within heart chambers to the heart muscle. This contrasts with the human heart, which is supplied by coronary vessels receiving blood from the aorta. Positive results have been demonstrated in some human patients receiving PMR treatments. These results are believed to be caused in part by blood flowing from within a heart chamber through patent channels formed by PMR to the myocardial tissue. Suitable PMR holes have been burned by laser, cut by mechanical means, and burned by radio frequency current devices. Increased blood flow to the myocardium is also believed to be caused in part by the healing response to wound formation. Specifically, the formation of new blood vessels is believed to occur in response to the newly created wound.
The present invention pertains to a device and method for performing percutaneous myocardial revascularization (PMR). The device of the present invention can be used to form crater wounds in the myocardium of the patient""s heart. A crater wound can be viewed as a wound having a width greater than its depth, whereas a channel wound is one having a depth greater than its width. A hole in the myocardium is a volumetric removal of tissue. The device can also be used to form channel wounds, but the configuration of the device""s electrode(s) makes the device particularly suitable for creating crater wounds.
In the preferred form of the method in accordance with the present invention, a crater wound is made through the endocardium and into the myocardium. The wound, and thus the healing response, including angiogenisis and subsequent perfusion of tissue is enhanced by collateral damage to the myocardium. The collateral damage is preferably induced by directing pressurized saline, contrast media, drug or a combination into the crater site through the endocardium and into the myocardium. This causes the vessels, capillaries and sinuses to rupture. By creating the collateral damage, the number of wounds which need to be made during the PMR procedure can be substantially reduced as the size of each wound is increased in view of the collateral damage. Additionally, and arguably as significant as the reduction in the number of wounds which must be formed during the procedure, is the reduction of the likelihood of a myocardial perforation. This reduction is possible because the holes can be limited in depth to just through the endocardium. Once the endocardium is perforated, pressure from infused fluid can rupture the myocardial vessels without further ablation or removal of tissue.
In a preferred embodiment, a catheter in accordance with the present invention includes an elongate shaft having a proximal end and a distal end, and a conductor extending therethrough. An electrode is disposed at the distal end of the shaft and connected to the conductor. The electrode has a generally annular transverse crosssectional shape. The annular shape defines an opening within the electrode. An insulator surrounds the elongate shaft.
A stop is disposed in the opening a predetermined distance proximally of the distal end of the electrode. The shaft preferably defines a lumen in fluid communication with the opening through the electrode. In one embodiment, a needle can be disposed within the opening and be in fluid communication with the lumen to deliver contrast media, growth factors or drugs to the wound.
In another embodiment, the annular shape of the electrode is generally circular. The annular shape can be continuous or in an alternate embodiment, discontinuous and formed from a plurality of discrete electrodes positioned in an array. The electrode can also include a serrated edge that produces a plurality of electrode contact points.
A method for performing PMR in accordance with the present invention includes providing a catheter having an elongate shaft including a proximal end and a distal end. A generally annular shaped electrode is disposed at the distal end of the shaft. The electrode is advanced to proximate the endocardial surface of the myocardium of the patient""s heart. The electrode is energized and advanced into the myocardium to form an annular shaped crater wound. Depth is controlled by a mechanical stop.